This proposal will examine the hypothesis that comprehensive mapping of endocardial and epicardial monophasic action potential distribution will permit accurate prediction of body surface potential maps during QRST. It will also examine the alternate hypothesis that failures of prediction stem primarily from intramural effects of anisotropy of heart muscle, inhomogeneity of the volume conduction. The data collected will include serial monophasic action potential maps of endocardial and epicardial surfaces, body surface potential maps, experimentally determined transfer coefficients from heart-to-skin. The analysis will include the construction of models of the heart-in-torso, of comparing alternative methods of information transfer between heart surface and body surface, and of combining these approaches to provide serial instantaneous display of the heart's electrical activity in image form. Better understanding of the mixture and integration of the flow of information (electrical signal) from the heart to the body surface may provide the proper critical background for subsequent revision of diagnostic systems based on surface pattern analysis. Organization of the surface phase relationships under normal and common abnormal conditions provide the matrix upon which a dynamic image of the probable electrical state of the ventricular wall may be built; such a display - especially when correlated with other cardiac imaging techniques - should accelerate accumulation of insight into the relationship between electrical and mechanical cardiac function.